Audio component systems are already in wide use which comprise a plurality of audio components such as a tuner, CD player, tape recorder and MD player as connected to one another.
For example, FIG. 4 shows an audio component system which comprises audio components, i.e., a tuner 20, CD player 30, tape recorder 40 and MD player 50, which are connected to an amplifier unit 9. A speaker 6 is connected to the output terminal of the amplifier unit 9 for delivering as its sound output an audio signal sent out from one audio output component selected by the amplifier unit 9, e.g., from the CD player 30. Further one audio output component selected by the amplifier unit 9, e.g., the tuner 20, feeds an audio signal to one audio input component, e.g., to the MD player 50, which records the audio signal.
The amplifier unit 9 has a plurality of signal input terminals a, b, c, d having connected thereto signal output lines 81 to 84 extending from the audio output components, and a plurality of signal output terminals e, f having connected thereto signal input lines 85, 86 extending from the audio input components.
The signal input terminals a, b, c and d are connected via a selector 91 to a signal processing system comprising a preamplifier 92, audio signal processing circuit 93 and post amplifier 94, and an audio signal is delivered to the speaker 6 via the signal processing system. The output terminal of the preamplifier 92 is connected to the signal output terminals e, f through a plurality of on-off switches 95, 96, and an audio signal is delivered from the terminal e or f to the tape recorder 40 or MD player 50.
The selector 91 and the on-off switches 95, 96 are controlled by a control circuit 98 to realize an operation in accordance with the manipulation of an input unit 97 by the user. For example, when the audio signal to be produced by the CD player 30 is to be recorded on an MD (mini disk) by the MD player 50, the input unit 97 is manipulated to select the CD player 30 as a signal output component and the MD player 50 as a signal input component, whereupon the selector 91 is switched to the input terminal connected to the CD player 30, the on-off switch 95 connected to the tape recorder 40 is opened, and the on-off switch 96 connected to the MD player 50 is closed.
Consequently, the audio signal from the CD player 30 is fed to the MD layer 50 by way of the selector 91, preamplifier 92 and on-off switch 96 and recorded on the MD.
With the conventional audio component system described, however, the signal output lines 81 to 84 and the signal input lines 85, 86 each comprise three conductors, i.e., a right-channel signal conductor, left-channel signal conductor and ground conductor. Accordingly, for example when the connection of the four audio components 20, 30, 40, 50 are to be connected to the amplifier unit 9 as illustrated, there is a need to use twelve signal conductors in all, and the amplifier unit 9 needs to be provided with twelve signal input or output terminals for the connection of these twelve signal conductors. The numbers of the signal conductors and signal input or output terminals required increase with an increase in the number of audio components providing the system.
As a result, the signal input and output terminal portions of the amplifier unit 9 occupy an increased area, not only making the amplifier unit 9 greater in size but also entailing the problem of an increased parts cost due to the increase in the number of signal conductors or lines and the problem of a cumbersome signal line connecting procedure by the user.